Darren Dietz was born on July 17, 1993, in Medicine Hat, Alberta. He played junior hockey with the Saskatoon Blades of the Western Hockey League and was selected in the fifth round of the 2011 NHL Entry Draft by the Montreal Canadiens.

Dietz made his professional debut for the Canadiens's AHL affiliate, the Hamilton Bulldogs, during the 2013-14 season. He would appear in 34 games for the club, recording five assists.

Dietz would spend the majority of the 2015-16 season with the Canadiens' new AHL affiliate, the St. John's IceCaps. He would see action in 61 games, scoring four times and adding 12 assist. Dietz would also get his first glimpse of life in the NHL during the 2015-16 season, suiting up in 13 games for the Canadiens, recording a goal and four assists.

On July 1, 2016, as an unrestricted free agent, Dietz signed with the Washington Capitals.